1. Field of the Invention
The present invention relates to a recording medium. More specifically, it relates to a recording medium suitable for use in an optical disc having a high photosensitivity and a high signal-to-noise (S/N) ratio.
2. Description of the Prior Art
Recent rapid progress in optical techniques have led to the development and use of optical discs capable of recording information at a high recording density. In the art, information is recorded in a recording layer formed on the surface of a substrate by using laser beams or other photobeams to open information holes (i.e., pits) in the layer. The recorded information is read out (or detected), based on the presence or absence of pits in the recording layer, by irradiating a photobeam onto the recording layer.
Known recording media for use in optical discs (referred to hereinafter as "the recording medium or media") comprises a thin film of a simple substance such as bismuth (Bi) or tellurium (Te) formed as a recording layer on the surface of a substrate by, for example, a standard vapor deposition technique. Conventional recording media, however, have several disadvantages. First, existing semiconductor lasers, which have relatively small power, cannot easily be used for the recording of information from the viewpoint of photosensitivity. Second, the media's signal-to-noise (S/N) ratio is low, making information difficult to reproduce at a high quality. For instance, when information is recorded at an optical disc speed of 1800 rpm in a recording layer composed of Te formed on a poly(methyl methacrylate) substrate using a laser beam having a power of 17 to 18 mW at the surface of the optical disc, the S/N ratio of the reproducing signal at a band width of 10 MHz is at most 38 dB.